Burn bootloader: Use programmer from any related platform (not just from the current platform)

Solve extremely slow load of projects with many files

Fix issue that prevented the sonoff project from building (also applies to other projects that use a more complex syntax for prototypes)

Automatically include all source code when an existing arduino project is first opened. This ensures new users can see header files in project sub folders (previously only \src and below where automatically added)

Atmel studio resolve board options for intellisense and also to ensure the correct mcu device is set for the project. Cores such as MiniCore resolve {board.mcu} from the variant specified by the board options.